A helicopter involved in a fatal crash in Western Australia’s Wheatbelt broke apart mid-flight, Australia’s aviation safety watchdog has found.

Two men, one aged in his 50s and one in his 70s, were killed when the Robinson R22 helicopter crashed just outside of Koorda on October 2, 2022.

The men had been taking part in a social flying event and were on their way from Koorda to Perth’s Jandakot airport.

In its final report released on Tuesday the Australian Transport Safety Bureau (ATSB) found the in-flight break-up occurred shortly after the two-seater helicopter reached cruise altitude, six minutes after taking off.

The aircraft crashed at Cowcowing Lakes shortly after.

The helicopter was destroyed, but based on an examination of the wreckage the ATSB found the aircraft had stalled mid-flight.

The agency said it was a “low rotor RPM” stall, where the main rotor can no longer produce enough lift to support the weight of the helicopter.

If not quickly and effectively managed it can reduce rotation to the point where one or both main rotor blades stall.

The bureau said this, along with delayed or inappropriate control inputs, resulted in “extreme teetering” of the main rotor assembly and subsequent in‑flight break-up.

Other factors identified

The ATSB could not confirm why the helicopter experienced the break-up, but highlighted the need for pilots to be able to identify and quickly apply the correct flight control inputs to recover from it.

However, a safety notice from the helicopter manufacturer cited in the report warned recovery from a low RPM rotor stall was “virtually impossible”.

Other contributing factors identified included the pilot’s failure to disclose a medical condition, his use of prescription medication, and the installation of dual flight controls in the helicopter.

The ATSB also said the quick-disconnect dual flight controls were installed on the passenger side, increasing the risk of inadvertent passenger control.

The bureau recommended these controls be removed so passengers do not accidentally interfere with the piloting of the plane.

It also said in-flight video recording would help better determine the cause of similar accidents.